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From: Joe Damato <jdamato@fastly.com>
To: linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org
Cc: chuck.lever@oracle.com,
	jlayton@kernel.org,
	linux-api@vger.kernel.org,
	brauner@kernel.org,
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	davem@davemloft.net,
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	sridhar.samudrala@intel.com,
	kuba@kernel.org,
	willemdebruijn.kernel@gmail.com,
	weiwan@google.com,
	David.Laight@ACULAB.COM,
	arnd@arndb.de,
	Joe Damato <jdamato@fastly.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jan Kara <jack@suse.cz>,
	linux-fsdevel@vger.kernel.org (open list:FILESYSTEMS (VFS and infrastructure))
Subject: [PATCH net-next v4 2/3] eventpoll: Add per-epoll busy poll packet budget
Date: Wed, 31 Jan 2024 01:47:32 +0000
Message-Id: <20240131014738.469858-3-jdamato@fastly.com>
In-Reply-To: <20240131014738.469858-1-jdamato@fastly.com>
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When using epoll-based busy poll, the packet budget is hardcoded to
BUSY_POLL_BUDGET (8). Users may desire larger busy poll budgets, which
can potentially increase throughput when busy polling under high network
load.

Other busy poll methods allow setting the busy poll budget via
SO_BUSY_POLL_BUDGET, but epoll-based busy polling uses a hardcoded
value.

Fix this edge case by adding support for a per-epoll context busy poll
packet budget. If not specified, the default value (BUSY_POLL_BUDGET) is
used.

Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 fs/eventpoll.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index ce75189d46df..3985434df527 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -229,6 +229,8 @@ struct eventpoll {
 	unsigned int napi_id;
 	/* busy poll timeout */
 	u64 busy_poll_usecs;
+	/* busy poll packet budget */
+	u16 busy_poll_budget;
 #endif
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -437,10 +439,14 @@ static bool ep_busy_loop_end(void *p, unsigned long start_time)
 static bool ep_busy_loop(struct eventpoll *ep, int nonblock)
 {
 	unsigned int napi_id = READ_ONCE(ep->napi_id);
+	u16 budget = READ_ONCE(ep->busy_poll_budget);
+
+	if (!budget)
+		budget = BUSY_POLL_BUDGET;
 
 	if ((napi_id >= MIN_NAPI_ID) && ep_busy_loop_on(ep)) {
 		napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep, false,
-			       BUSY_POLL_BUDGET);
+			       budget);
 		if (ep_events_available(ep))
 			return true;
 		/*
@@ -2098,6 +2104,7 @@ static int do_epoll_create(int flags)
 	}
 #ifdef CONFIG_NET_RX_BUSY_POLL
 	ep->busy_poll_usecs = 0;
+	ep->busy_poll_budget = 0;
 #endif
 	ep->file = file;
 	fd_install(fd, file);
-- 
2.25.1